The QMessageBox class provides a modal dialog with a short message, an icon, and some buttons.

Message boxes are used to provide informative messages and to ask simple questions.

QMessageBox provides a range of different messages, arranged roughly along two axes: severity and complexity.

Severity is <center>.nf

Complexity is one button (OK) for simple messages, or two or even three buttons for questions.

There are static functions for the most common cases.

Examples:

.)l

If a program is unable to find a supporting file, but can do perfectly well without it:

.nf

QMessageBox::information( this, "Application name",

"Unable to find the user preferences file.\n"

"The factory default will be used instead." );

.fi

question() is useful for simple yes/no questions:

.nf

if ( QFile::exists( filename ) &&

QMessageBox::question(

this,

tr("Overwrite File? -- Application Name"),

tr("A file called %1 already exists."

"Do you want to overwrite it?")

.arg( filename ),

tr("&Yes"), tr("&No"),

QString::null, 0, 1 ) )

return false;

.fi

warning() can be used to tell the user about unusual errors, or errors which can't be easily fixed:

.nf

switch( QMessageBox::warning( this, "Application name",

"Could not connect to the <mumble> server.\n"

"This program can't function correctly "

"without the server.\n\n",

"Retry",

"Quit", 0, 0, 1 ) ) {

case 0: // The user clicked the Retry again button or pressed Enter

// try again

break;

case 1: // The user clicked the Quit or pressed Escape

// exit

break;

}

.fi

The text part of all message box messages can be either rich text or plain text. If you specify a rich text formatted string, it will be rendered using the default stylesheet. See QStyleSheet::defaultSheet() for details. With certain strings that contain XML meta characters, the auto-rich text detection may fail, interpreting plain text incorrectly as rich text. In these rare cases, use QStyleSheet::convertFromPlainText() to convert your plain text string to a visually equivalent rich text string or set the text format explicitly with setTextFormat().

Note that the Microsoft Windows User Interface Guidelines recommend using the application name as the window's caption.

Below are more examples of how to use the static member functions. After these examples you will find an overview of the non-static member functions.

Exiting a program is part of its normal operation. If there is unsaved data the user probably should be asked if they want to save the data. For example:

.nf

switch( QMessageBox::information( this, "Application name here",

"The document contains unsaved changes\n"

"Do you want to save the changes before exiting?",

"&Save", "&Discard", "Cancel",

0, // Enter == button 0

2 ) ) { // Escape == button 2

case 0: // Save clicked or Alt+S pressed or Enter pressed.

// save

break;

case 1: // Discard clicked or Alt+D pressed

// don't save but exit

break;

case 2: // Cancel clicked or Escape pressed

// don't exit

break;

}

.fi

The Escape button cancels the entire exit operation, and pressing Enter causes the changes to be saved before the exit occurs.

Disk full errors are unusual and they certainly can be hard to correct. This example uses predefined buttons instead of hard-coded button texts:

.nf

switch( QMessageBox::warning( this, "Application name here",

"Could not save the user preferences,\n"

"because the disk is full. You can delete\n"

"some files and press Retry, or you can\n"

"abort the Save Preferences operation.",

QMessageBox::Retry | QMessageBox::Default,

QMessageBox::Abort | QMessageBox::Escape )) {

case QMessageBox::Retry: // Retry clicked or Enter pressed

// try again

break;

case QMessageBox::Abort: // Abort clicked or Escape pressed

// abort

break;

}

.fi

The critical() function should be reserved for critical errors. In this example errorDetails is a QString or const char*, and QString is used to concatenate several strings:

.nf

QMessageBox::critical( 0, "Application name here",

QString("An internal error occurred. Please ") +

"call technical support at 1234-56789 and report\n"+

"these numbers:\n\n" + errorDetails +

"\n\nApplication will now exit." );

.fi

In this example an OK button is displayed.

QMessageBox provides a very simple About box which displays an appropriate icon and the string you provide:

If you want your users to know that the application is built using Qt (so they know that you use high quality tools) you might like to add an "About Qt" menu option under the Help menu to invoke aboutQt().

If none of the standard message boxes is suitable, you can create a QMessageBox from scratch and use custom button texts:

.nf

QMessageBox mb( "Application name here",

"Saving the file will overwrite the original file on the disk.\n"

"Do you really want to save?",

QMessageBox::Information,

QMessageBox::Yes | QMessageBox::Default,

QMessageBox::No,

QMessageBox::Cancel | QMessageBox::Escape );

mb.setButtonText( QMessageBox::Yes, "Save" );

mb.setButtonText( QMessageBox::No, "Discard" );

switch( mb.exec() ) {

case QMessageBox::Yes:

// save and exit

break;

case QMessageBox::No:

// exit without saving

break;

case QMessageBox::Cancel:

// don't save and don't exit

break;

}

.fi

QMessageBox defines two enum types: Icon and an unnamed button type. Icon defines the Question, Information, Warning, and Critical icons for each GUI style. It is used by the constructor and by the static member functions question(), information(), warning() and critical(). A function called standardIcon() gives you access to the various icons.

The text(), icon() and iconPixmap() functions provide access to the current text and pixmap of the message box. The setText(), setIcon() and setIconPixmap() let you change it. The difference between setIcon() and setIconPixmap() is that the former accepts a QMessageBox::Icon and can be used to set standard icons, whereas the latter accepts a QPixmap and can be used to set custom icons.

Opens a critical message box with the caption caption and the text text. The dialog may have up to three buttons. Each of the button parameters, button0, button1 and button2 may be set to one of the following values:

QMessageBox::NoButton

QMessageBox::Ok

QMessageBox::Cancel

QMessageBox::Yes

QMessageBox::No

QMessageBox::Abort

QMessageBox::Retry

QMessageBox::Ignore

QMessageBox::YesAll

QMessageBox::NoAll

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

One button can be OR-ed with QMessageBox::Default, and one button can be OR-ed with QMessageBox::Escape.

Returns the identity (QMessageBox::Ok, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Displays a critical error message box with a caption, a text, and 1, 2 or 3 buttons. Returns the number of the button that was clicked (0, 1 or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional, and button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1; supply 0, 1, or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

Opens an information message box with the caption caption and the text text. The dialog may have up to three buttons. Each of the buttons, button0, button1 and button2 may be set to one of the following values:

QMessageBox::NoButton

QMessageBox::Ok

QMessageBox::Cancel

QMessageBox::Yes

QMessageBox::No

QMessageBox::Abort

QMessageBox::Retry

QMessageBox::Ignore

QMessageBox::YesAll

QMessageBox::NoAll

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

One button can be OR-ed with QMessageBox::Default, and one button can be OR-ed with QMessageBox::Escape.

Returns the identity (QMessageBox::Ok, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Displays an information message box with caption caption, text text and one, two or three buttons. Returns the index of the button that was clicked (0, 1 or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional. button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1; supply 0, 1 or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

Note: If you do not specify an Escape button then if the Escape button is pressed then -1 will be returned. It is suggested that you specify an Escape button to prevent this from happening.

Opens a question message box with the caption caption and the text text. The dialog may have up to three buttons. Each of the buttons, button0, button1 and button2 may be set to one of the following values:

QMessageBox::NoButton

QMessageBox::Ok

QMessageBox::Cancel

QMessageBox::Yes

QMessageBox::No

QMessageBox::Abort

QMessageBox::Retry

QMessageBox::Ignore

QMessageBox::YesAll

QMessageBox::NoAll

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

One button can be OR-ed with QMessageBox::Default, and one button can be OR-ed with QMessageBox::Escape.

Returns the identity (QMessageBox::Yes, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Displays a question message box with caption caption, text text and one, two or three buttons. Returns the index of the button that was clicked (0, 1 or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional. button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1; supply 0, 1 or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

Note: If you do not specify an Escape button then if the Escape button is pressed then -1 will be returned. It is suggested that you specify an Escape button to prevent this from happening.

Returns the pixmap used for a standard icon. This allows the pixmaps to be used in more complex message boxes. icon specifies the required icon, e.g. QMessageBox::Question, QMessageBox::Information, QMessageBox::Warning or QMessageBox::Critical.

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

Returns the pixmap used for a standard icon. This allows the pixmaps to be used in more complex message boxes. icon specifies the required icon, e.g. QMessageBox::Information, QMessageBox::Warning or QMessageBox::Critical.

Opens a warning message box with the caption caption and the text text. The dialog may have up to three buttons. Each of the button parameters, button0, button1 and button2 may be set to one of the following values:

QMessageBox::NoButton

QMessageBox::Ok

QMessageBox::Cancel

QMessageBox::Yes

QMessageBox::No

QMessageBox::Abort

QMessageBox::Retry

QMessageBox::Ignore

QMessageBox::YesAll

QMessageBox::NoAll

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

One button can be OR-ed with QMessageBox::Default, and one button can be OR-ed with QMessageBox::Escape.

Returns the identity (QMessageBox::Ok, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Displays a warning message box with a caption, a text, and 1, 2 or 3 buttons. Returns the number of the button that was clicked (0, 1, or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional, and button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1; supply 0, 1, or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

Note: If you do not specify an Escape button then if the Escape button is pressed then -1 will be returned. It is suggested that you specify an Escape button to prevent this from happening.

The icon of the message box can be one of the following predefined icons:

QMessageBox::NoIcon

QMessageBox::Question

QMessageBox::Information

QMessageBox::Warning

QMessageBox::Critical

The actual pixmap used for displaying the icon depends on the current GUI style. You can also set a custom pixmap icon using the QMessageBox::iconPixmap property. The default icon is QMessageBox::NoIcon.

See also iconPixmap.

Set this property's value with setIcon() and get this property's value with icon().

The text will be interpreted either as a plain text or as rich text, depending on the text format setting (QMessageBox::textFormat). The default setting is AutoText, i.e. the message box will try to auto-detect the format of the text.

The default value of this property is QString::null.

See also textFormat.

Set this property's value with setText() and get this property's value with text().

The definitive Qt documentation is provided in HTML format; it is located at $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.

If you find errors in this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qmessagebox.3qt) and the Qt version (3.3.8).